This proposal is submitted in response to the announcement `NIH Small grant Program (RO3)-PA- 06-180'. The goal of this proposal is to understand the role of transcription antitermination and melting of nucleic acid secondary structures in bacterial adaptation to physiologically low temperatures. In Escherichia coli, a number of proteins are induced upon temperature downshift. E. coli CspA, the major cold shock protein, is one of the nine homologous proteins present in E. coli. Several characterized members of the family, including CspA, function as `RNA chaperones'and destabilize secondary structures in RNA thus antiterminating transcription and promoting transcription elongation at low temperature. Stabilization of secondary structures in mRNA also impairs translation, however the mechanisms operating there have not been defined. The CspA family proteins consist of a Cold Shock Domain (CSD), which belongs to the OB (oligomer binding) fold, a superfamily that also includes S1 domain-containing proteins. I hypothesize that structural similarity between S1 and CSD domains leads to functional similarity and that some S1 domain proteins may participate in cold shock acclimation. The specific aims of the present proposal are (i) Perform comparative structure-functional analysis of all 9 E. coli members of the CspA family with respect to their ability to melt nucleic acid secondary structures, perform transcription antitermination and function in cold acclimation. (ii) Perform structure-functional analysis of certain model E. coli S1 domain proteins such as IF1, PNPase and ribosomal protein S1 with respect to their ability to melt nucleic acids secondary structures, perform transcription antitermination, stimulate translation and elucidate physiological consequences of such functions. The proposed work will lead to a deeper understanding of cell adaptation to cold shock and may reveal that there exists a cross-talk and/or functional overlap between the Csp family proteins, known to be involved in transcription regulation at cold shock, and S1 domain proteins known to function in translation. Relevance in public health: Bacterial food-borne pathogens that contaminate refrigerated foods must be able to undergo efficient cold shock response. The present proposal will help identify key factors essential for effective cold shock response, and may thus uncover ways to regulate it. This knowledge will be highly significant for basic science, as well as for the medical field.